Seeing polarised light

Unlike the animals described above, humans are largely polarisation-blind. However, some individuals may be able to perceive a polarisation effect known as Haidinger’s brush.

This appears as a tiny, yellowish figure-of-eight-shaped image about 3° in longitudinal diameter that may be seen in highly polarised light. It is suggested that the effect is most easily seen at the zenith of a clear sky, near sunset and sunrise. After a couple of minutes of observing, the sky may take on a marbled appearance and the brush should appear as a subtle mark against the sky.

Some people find the effect easier to observe than others. It can also be seen by observing a computer screen through a polarising filter for a couple of seconds and then quickly rotating the polaroid. The effect arises because pigments in the macula of the retina have a radial arrangement and linearly polarised light is absorbed more strongly in some parts of the pigments than others, causing a visible effect when the direction of polarisation of light is suddenly changed.